二维数组根据某列值归类

// 原数组：
 
[
    {
        "province": "河北省",
        "city": "石家庄市"
    },
    {
        "province": "河北省",
        "city": "衡水市"
    },
    {
        "province": "山西省",
        "city": "太原市"
    },
    {
        "province": "山西省",
        "city": "吕梁市"
    }
]


//期望数组：
[
    {
        "province": "河北省",
        "city": [
            "石家庄市",
            "衡水市"
        ]
    },
    {
        "province": "山西省",
        "city": [
            "太原市",
            "吕梁市"
        ]
    }
]

　　

Coding:

        $jsonStr = '[
                    {
                        "province": "河北省",
                        "city": "石家庄市"
                    },
                    {
                        "province": "河北省",
                        "city": "衡水市"
                    },
                    {
                        "province": "山西省",
                        "city": "太原市"
                    },
                    {
                        "province": "山西省",
                        "city": "吕梁市"
                    }
                   ]';
        $list = json_decode($jsonStr, true);
        $nList = [];
        foreach ($list as $val) {
            if (isset($nList[$val['province']])) {
                $nList[$val['province']]['city'][] = $val['city'];
            } else {
                $nList[$val['province']]['province'] = $val['province'];
                $nList[$val['province']]['city'][] = $val['city'];
            }
        }

        echo json_encode(array_values($nList));